Plate 5. 



Endoparasitic development of Sacculina neglecla. 



The plane which Insects the mesentery longitudinally is spoken of as the longitudinal plane; the plane 

 transverse to this as transverse. — The parts of sections tinted red belong to the host. 



app abdominal appendages of crab, has basilar membrane of Sacculina. be brood pouch or mantle 

 cavity, b.sac body of Sacculina. eg colleteric gland, eh chitin. ck.ext external chitin of thorax of crab. 

 co?' blood corpusculus of crab, c.t central tumour, ct.cav cavity of central tumour, div.inf inferior diver- 

 ticulum of gut of crab, div.sup superior diverticulum of gut of crab, epl internal epithelium of brood pouch. 

 ep2 external epithelium of brood pouch. ep3 internal epithelium of perisomatic cavity. ep4 external epi- 

 thelium of perisomatic cavity, ext.ep external ectoderm of crab, gn nervous ganglion, gut gut of crab. 

 / epithelium of root, liv liver diverticulum of crab, mes mesentery, m muscle cells, m.c mesenchymatous 

 cells, muse muscular layer, mus.l longitudinal musculature, mus.t transverse muscles of mantle, musc.c 

 circular muscles of mantle. u "nucleus" or body rudiment of Sacculina. op opening of perisomatic cavity. 

 ov ovary, p.c perisomatic cavity, r roots of Sacculina. sp spider cells. t testes, v.d vas deferens. 

 x definitive position on crab's gut of adult Sacculina body. 



Fig. 1. Upper part of gut of Inachus scorpio, near stomach, with a Sacculina interna migrans (sac) attached 

 to liver diverticulum. X 23. 



Fig. 2. Mid-gut of Inachus scorpio. Sacculina a little lower than in Fig. 1. X 23. 



Fig. 3. Section, slightly oblique, through Sacculina of Fig. 2. X 140. 



Fig. 4. Same as Fig. 3, a small portion greatly enlarged. X 650. 



Fig. 5. Mid-gut of I. scorpio, with Sacculina growing down towards definitive position (x)\ nucleus (n) 

 already differentiated. X 23. 



Fig. G. Section through tumour and nucleus of Sacculina of Fig. 5. X 650. 



Fig. 7. Section through tumour and nucleus of a Sacculina interna. Later stage than Fig. 6. X 325. 



Fig. 8. Mid-gut of I. scorpio with Sacculina attaining to definitive position x. X 23. 



Fig. 9. Section through tumour and nucleus of Sacculina of Fig. 8. X 325. 



Fig. 10. Longitudinal section through gut and ventral wall of thorax of I. scorpio with a Sacculina interna 

 in definitive position, showing that the parasite is completely internal at this stage. X 7 0. 



Fig. 10a. Mid-gut of I. scorpio with Sacculina interna in definitive position, ready to come out. Only some 

 of the roots are drawn. X 23. 



Fig. 11. Longitudinal section through mesenterial plane of Sacculina interna to show formation of peri- 

 somatic cavity (]).c) by means of invagination. X 325. 



Fig. 12. Horizontal section through central tumour and developing body of Sacculina to show further deve- 

 lopment of perisomatic cavity. X 140. 



Fig. 13. Same as 12, but deeper section; and more enlarged to show histology of development. X 325. 



Fig. 14. Transverse section through a later stage, showing perisomatic cavity (p.c) fully developed. X 140. 



Fig. 15. Transverse section through middle of body of Sacculina interna, late stage, to show development 

 of testis. Tumour and perisomatic cavity and mantle omitted. X 650. 



Fig. 16. Same as 15, but still later stage; Sacculina ready to be evaginated. Showing development of 

 colleteric glands (eg). X 45. 



Fig. 17. Transverse section of portion of body of Sacculina of about same age as Fig. 14, to show formation 

 of nervous ganglion (g.u) from outer wall of brood cavity (b.c). X 325. 



Fig. 18. Section through the root of a Sacculina interna. X 650. 



